The invention relates to an apparatus for coating a substrate, preferably with aluminum oxide, having a direct-current and/or an alternating-current source which is connected to an electrode disposed in an evacuable coating chamber which is connected electrically with a target which is sputtered and whose sputtered particles precipitate upon the substrate, such as a plastic piece. The coating chamber can be charged with a process gas, and toroidal magnetic fields pass through the target and their lines of force issue from the surface of the target in the area of the magnetic poles.
A cathode sputtering apparatus is known (German Patent Disclosure Document 27 07 144; Sloan Technology Corp.). It has a cathode which bears a surface to be sputtered, a magnet system near the cathode and at the side confronting the surface to be sputtered for the production of magnetic lines of force, at least some of which enter the surface to be sputtered and issue again therefrom, namely at intersection points lying at a distance from one another, between which the lines of force continuously form arcuate segments at a distance from the surface to be sputtered. The latter -- together with the lines of force -- form a boundary for a confined area whereby a tunnel-like area is formed, which lies over a path thereby defined on the surface to be sputtered. Charged particles tend to be held back in the tunnel-like area and to move along it. The apparatus also has an anode adjacent to the cathode, and the cathode and anode are connected to a source of electrical potential. At least the surface to be sputtered is situated within an evacuable container.
In this apparatus a driving means is provided for producing relative movement between the magnetic field and the surface to be sputtered, while retaining its spatial proximity. The abovementioned path runs across the surface to be sputtered, covering a surface area which is greater than the surface area occupied by the path at rest.
Also known (P 38 21 207.2, to which U.S. Pat. No. 4,931,169; corresponds Leybold AG) is a system for coating a substrate with dielectrics. It has a direct-current source which is connected to an electrode that is in electrical communication with a target which is sputtered, and whose sputtered particles enter into a compound with the delivered material, which precipitates on the substrate. Toroidal magnetic fields pass through the target and their lines of force issue from the surface of the target at the magnet poles. In this system an alternatingcurrent source is provided, whose output voltage is superimposed on the direct voltage of the direct-current source, while the electrical power of the alternating current source that is fed to the electrode corresponds to 5% to 25% of the power fed by the direct-current source to the electrode.
Lastly, in an older patent application Ser. No. (P 39 29 695.4, to which U.S. Pat. No. 5,026,471 corresponds) an apparatus for coating a substrate has been proposed, which is equipped with a direct-current and/or an alternating-current source connected to an electrode which is disposed in an evacuable coating chamber and electrically connected to a target which is sputtered and whose sputtered particles deposit themselves on the substrate. A process gas can be put into the coating chamber and magnetic fields pass through the target with their lines of force issuing from the surface of the target in the area of the magnetic poles.
In this apparatus the target has two substantially elongated, parallelepipedal portions, the ends of the two portions being joined by means of two arcuate target portions and thus together forming a ring-like or oval target.
The target in this apparatus is surrounded by a dark-space shielding whose circumferential margin or end surface facing the substrate is slightly set back from the front surface of the target. The magnet system disposed in a cathode tub and held on a yoke is composed of a central row of narrow magnets extending in the lengthwise direction of the target, an additional endless series of narrow magnets disposed at the marginal portion of the yoke, and two round magnets, one of the round magnets being located at each end of the central row of magnets.